It has now been recognized that the world's environment is suffering too much from global warming caused by greenhouse gas exposure in the atmosphere. To address this problem governments are now starting to adopt targets for reducing the emission of greenhouse gases to the environment and play their part to address this problem for future generations. While some countries have not adopted a firm goal, other countries, for example Australia, have adopted a policy for the reducing greenhouse gases by 20% by the year 2020.
Greenhouse gases can be emitted from cars, industry, farming, and households to name a few. While certainly not as apparent as a large factory with tall smokestacks, within a normal household the gas burning appliances, such as furnaces, water heaters, etc., all release such greenhouse gases as a by-product of the combustion process itself. While the appliance industry has taken a leading role in energy efficiency and environmental concern, further improvement is always foremost in mind of the appliance design engineer.
With such further improvement in mind, especially with the increased awareness of global climate change and changing governmental regulations, it is noted that hot water heaters, both internal and externally installed units, can be one of the more fairly inefficient appliances in energy conservation, and therefore require the burning of additional fuel to maintain the set point temperature. This, of course, results in the additional production of greenhouse gas beyond that which a more efficient appliance would produce.
A typical hot water heater includes a vertical tank with a centrally located flue pipe. A gas burner is positioned underneath the tank and is controlled by a combination gas controller. The combination gas controller incorporates an On/Off valve, a pilot safety circuit, pilot and main burner pressure regulators and their associated supply pipe connections, as well as a thermostat to control the hot water heater to maintain the water in the storage tank at a predetermined temperature.
Upon the thermostat calling for more heat, the main gas valve opens to allow gaseous fuel (gas) to flow to the main burner where it is ignited by the pilot light. Ignition and combustion of the gas results in hot flue gas being generated. The heat from the hot flue gases is transferred to the cold water via the bottom of the tank and through the walls of the central flue pipe. The flue gases exit out the top of the hot water heater.
There are generally two types of hot water heaters used throughout the world classified by their installation location. For an indoor water heater such as used in the North American market, the hot flue gases exit through a draft diverter that is connected to a flue pipe which pipes the flue gases safety to an outside location. Air for combustion of the gas is drawn into the combustion chamber at the bottom of the hot water heater. For an outdoor hot water heater such as used in the Australian market, the flue gases pass safely through a balanced flue terminal at the top of the heater to the outside atmosphere. The balanced flue terminal is so designed to allow a continuous supply of air for combustion irrespective whether the burner is on or off under all types of wind conditions. The air for combustion is transferred to the bottom of the heater internally within the appliance.
One of the current disadvantages for hot water heaters is the overall service efficiency of the appliances. Service efficiency is defined as the energy delivered to the hot water from the hot water heater each day, divided by the energy burnt in the gas to heat the water and to maintain the hot water in the tank at the desired temperature. The service efficiency may vary from around 0.50 or 50% for poor performing appliances, to appliances just complying to US regulations around 0.59, to superior products from 0.64 or 64% service efficiency. Low service efficiency may be due to poor thermal efficiency of the heat into the water when the burner is on and/or excessive heat losses when the burner is off.
While a small percentage of the heat loss may be caused by poor insulation from the outside of the tank, the majority of the losses are more likely a result of excessive losses from the hot primary flue pipe (heat exchanger) in the middle of the heater. This pipe is in contact with the hot water in the tank, and is designed to provide excellent heat transfer with the water to improve the “heat in” efficiency.
However, just as heat is transferred into the water when the burner is on, heat is also transferred out of the water when the burner is off. As a result of this standby heat loss, relatively cold air is continually being heated up and flows out of the hot water heater due to a thermo-syphoning effect by the flue pipe when the burner is off. Since the main burner is only on for one to two hours per day heating the stored water to keep it ready for use, the surfaces inside the flue pipe are exposed to the relatively cooler air for the remaining 22 hours. This natural cooling of the heated water via the flue pipe forces the thermostat to occasionally turn on the burner to continually top up the stored hot water to the desired temperature.
Recognizing this standby heat loss problem, there have been many attempts at providing some form of a flue damper that closes to limit the escape of heat through the flue pipe when the burner is turned off and that reliably opens to let the flue gases escape when the burner is on. Indeed, laboratory tests have proven that dampers can reduce the standby losses of a hot water heater by up to approx. 50%. This relates to approx. 500 Btu/h (0.50 Mj/h), which is a huge amount of energy considering the product life to 10 to 15 years. While such a damper could be electrically powered, such a damper would require additional power use and would need to be driven by a reliable supply. Gas powered dampers, that is dampers driven by the gas used for combustion, alleviate the problems of additional electrical power use and reliable supply. Unfortunately, the appliance industry generally and hot water heater manufacturers specifically have been frustrated by the fact that gas operated dampers “nearly work”. They are not popular and commonly have many problems and service issues.
One significant problem experienced by gas operated flue dampers relates to candling of the diminishing flame on shut down of conventional burners and low NOx burners. This candling effect results from the draining of the gas in the burner feed pipe that leads from the damper actuator valve to the burner after the burner has been commanded off. Since the gas operated damper valve is located on the flue pipe at the top of the hot water heater and the burner is located at the bottom, the gas pipe from the valve to the burner runs at least the length of the storage tank. As a result of the existence of gas in the pipe after the valve have been shut, a small flame at the injector continues to burn until the pipe is drained, which results in the gradual build up of soot on the burner. This, in turn, often results in poor combustion, further increasing the production of greenhouse and other dangerous gasses. Candling is especially a problem with installations where the gaseous fuel used is heavier than air such as propane, butane gas, etc.
To address the systemic problem of candling with prior gas operated dampers, some designs incorporate an additional damper valve bleed line, a flow orifice member, and a separate vent pilot. Unfortunately, such additional plumbing and components increase the complexity and cost of such systems, as well as reducing the overall reliability of the system due to the increase in components. In the highly cost competitive appliance industry, even with the overall lifetime cost of operation reduction and with the reduction in production of greenhouse gasses, such additional expense makes such hot water heaters undesirable by consumers.
Another problem with some gas controlled damper valves is that they can trap gas within the valving damper system. This often results in allowing the damper only partially to close the damper, reducing the energy savings by allowing some flow therethrough.
There is a need, therefore, for a gas operated damper system for gas burning appliances, such as a hot water heater, to reduce standby losses therefrom that overcomes the above described and other problems existing in the art. Embodiments of the invention provide such an energy savings damper system. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.